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Holy Smokes!


HighSkids
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Turbine on a 206LR was timed out so we swapped in the new one. Pushed it out for the leak check and everything was going great until about 1 to 1.5 minutes into the run heavy smoke started to billow out of the exhaust. We shut it down immediately. It burnt approx 1.5 litres of oil in about 15 to 20 seconds, which means a whole lot of smoke. After a thorough check of anything to do with the oil system we tried another run, but we got the same results. Same time into the run, same amazing discharge of smoke, same oil consumption. After a nap and some breakfast we swapped another turbine(that was designated for another machine still 50hrs away) and the problem disappeared. Any ideas? We're still waiting to hear back from the O/H shop.

 

The oil flow check before the initial run was 110cc.

 

And no, I didn't have a camera on hand.

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could be a #5 but that would be more on shutdown due... I vote for #8 seal.. either way it's a bad seal install or seal itself... We had a c20b once that was eating some serious oil.. not as bad as you are describing, and no cloud of smoke and it was a bad lab seal and it happened two times in a row... third time was a charm.

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Unlikely to be the #5Carbon seal is at fault. There can be numerous causes of a C20R smoking during operation. The usual culprits being the #1 carbon seal which in your case definitely not as the turbine swapped ruled that out the swap also ruled out the accessory gearbox scavenge pump. The O/H is likely to come back with one of 3 findings.

 

1. Scavenge struts in the GP and PT support at #6-7, #8 bearings, or 6-7 sump can are blocked either with carbon or some other debris preventing proper scavenge of the bearing sump area causing a pressurization of the sumps and oil leaking past the labrynth seals. ( a blocked PT scavenge strut is no where near as damaging to your turbine as blocked GP scavenge strut).

 

#2 A serious leak between the PT Sump Cover and the PT Support. Can be a machining error, bad crush seals, poor assembly procedure. ( The overhaul manual gives one specific procedure for assembling the PT sump Cover to the PT support but I have seen it performed numerous ways and have even seen some shops that apply sealent used for the gearbox splitlines on the crush seals at the Sump Cover to PT support seal locations an intersting method to say the least and not one approved by the OEM).

 

#3 A leak at the #8 bearing sump nut. This allows cooling air that flows into the turbine on the outside of the combustion liner through the GP struts into the cavity behind the first stage nozzle shield to flow into the number #8 oil sump. This pressurizes the #8 bearing cavity and forces oil out through the #8 lab seal and onto the #1 turbine wheel hub.

 

 

Obviously you have a huge amount of oil consumption and your oil flow check leads one to believe that there is no issue with blockage of scavenge struts as you would not get good Oil Flow results if the struts where blocked. Unless there was foriegn debris in the bearing sumps that was dislodged and blocked the struts after start up.

 

What I would be seriously concerened with is any leakage of oil past the #8 lab seal causing quenching of the #1 turbine wheel. Any evidence of oil being forcibly sprayed on the wheel during operation is cause for scrapping the wheel. With the amount of oil consumption you are experiencing I would be looking for some tear down photos from the shop. in particular I would want pics of the pt support and gp support and the evidence of where the oil is leaking in the turbine. It will be obvious to the overhaul shop where the oil is leaking into the gas path from as there will be a large amount of nice burnt shiny carbon in the area. Make sure to get a pic of the front of the #1 turbine wheel to be sure there was no oil quenching of the wheel itself. This will be evident by the wheel looking like someone has sprayed oil on it while running leaving what looks like a sunburst of burnt oil on the hub of the wheel.

 

Be sure to ask the shop that you are returning the turbine to to be 100% sure there is no oil quenching of the #1 wheel.

 

 

 

Turbinetech

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Thanks Turbine Tech. Word around the water cooler is the O/H shop thinks it was definately a seal issue, but could not explain the 1-2 minute lag for the smoke. Turns out it was rental turbine. It was returned to the owner off of a serviceable machine, and without inspection it was sent to us. Perhaps something lodged itself in a seal during removal/shipping.

 

If it was an improper installation of the PT sump would I still get the smoke out the exhaust stacks? That'd be an external leak.

 

Is it possible that the combustion liner could have cocked the heat sheild enough to let pressure in behind? That'd have to be a lot of distortion I imagine. Or is that complete nonsense?

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High Skids. Always nice when it isnt your turbine. #5 Carbon seals do not normally consume that much oil. One question to ask is how wet with oil was the exhaust collector when you removed the turbine? That is one definite indication of a #5 carbon seal failure. As you didnt mention any raw oil or puddling in the Turbine exhaust collector.

 

Referring to the PT sump. In this particular engine there is an external oil can at the 6-7 location designed to collect residual oil at shutdown this is commonly refered to as the PT sump can. Inside the guts of the turbine at the 6-7 bearing cavity is an assembly called the PT Sump Cover that is attached by bolts and sealed with 2 large crush seals to the hub of the PT support itself. When i was referring above to a leaking PT Sump Cover seals I was refering to the PT SUmp Cover inside the turbine and not on the outside. I understand your meaning though. How could an external leak cause that much smoke and consumption? It would be obvious where it was leaking and it wouldnt smoke much.

 

As far as your question about the combustion liner I saw many many years ago a combustion liner improperly installed cause very similar symptons that you describe so definitely not nonsense. The situation was exactly what you described a turbine with history of correct operation was assembled into an engine and installed in the aircraft after a difficult start the engine ran and promptly began to smoke like a mosquito fogger driven down the boulevards of Winnipeg. Turbine was removed and sent in to the shop for investigation. It was discovered that the #1 nozzle shield showed signs of distortion and appeared like the combustion liner was forced on. After calling the DOM at the operator it was discovered the combustion liner was bent, distorted, and crushed. From there it did not take long to realize that what had happened was the mechanic who built the engine had use the splitline bolts to draw down the combustion can to the GP support because he couldnt get the Combustion can to seat properly so instead of asking why he just tightened the nuts and moved on. This caused a leak of combustion gasses into the cooling air passges of the turbine and literally cooking the oil in the scavenge struts causing them to block, and oil to fill the #6-7 sump and overflow into the gas path. Where it burns and smokes. The design of the 250 trubine is such that the oil struts are surrounded by cooling air that moves through the cavity between the comb. can and the liner, so a the cocked combustion liner allowed combustion air to enter the cooling passages. With the result being severe oil consumption and smoking.

 

I really hope that makes sense to anyone besides me.

 

Turbinetech

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Just because you are getting a good oil flow does not mean all is right....I wrote this up before on this site....I had installed a freshly o/h turbine and did the oil flow check before run up and it was great...found out later after blowing a brand new 6&7 seal out that the oil return line from the sump can back to the gearbox was almost totally blocked with carbon buildup....check that return line after any new turbine install or any time the engine is out or if your oil is going black real quick :up: :) ps I would think you are having a 6&7 seal leak or as mentioned the #8 nut seal is the problem.... ;)

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